1. Field of the Invention
The present invention relates to a method of manufacturing a near-field light generator for use in thermally-assisted magnetic recording where a recording medium is irradiated with near-field light to lower the coercivity of the recording medium for data writing.
2. Description of the Related Art
Recently, magnetic recording devices such as magnetic disk drives have been improved in recording density, and thin-film magnetic heads and recording media of improved performance have been demanded accordingly. Among the thin-film magnetic heads, a composite thin-film magnetic head has been used widely. The composite thin-film magnetic head has such a structure that a read head including a magnetoresistive element (hereinafter, also referred to as MR element) for reading and a write head including an induction-type electromagnetic transducer for writing are stacked on a substrate. In a magnetic disk drive, the thin-film magnetic head is mounted on a slider that flies slightly above the surface of the magnetic recording medium.
To increase the recording density of a magnetic recording device, it is effective to make the magnetic fine particles of the recording medium smaller. Making the magnetic fine particles smaller, however, causes the problem that the magnetic fine particles drop in the thermal stability of magnetization. To solve this problem, it is effective to increase the anisotropic energy of the magnetic fine particles. However, increasing the anisotropic energy of the magnetic fine particles leads to an increase in coercivity of the recording medium, and this makes it difficult to perform data writing with existing magnetic heads.
To solve the foregoing problems, there has been proposed a technique so-called thermally-assisted magnetic recording. This technique uses a recording medium having high coercivity. When writing data, a magnetic field and heat are simultaneously applied to the area of the recording medium where to write data, so that the area rises in temperature and drops in coercivity for data writing. The area where data is written subsequently falls in temperature and rises in coercivity to increase the thermal stability of magnetization. Hereinafter, a magnetic head for use in thermally-assisted magnetic recording will be referred to as a thermally-assisted magnetic recording head.
In thermally-assisted magnetic recording, near-field light is typically used as a means for applying heat to the recording medium. A known method for generating near-field light is to apply laser light to a plasmon antenna, which is a small piece of metal, as described in U.S. Patent Application Publication No. 2008/0055762 A1, for example. The laser light applied to the plasmon antenna excites surface plasmons on the plasmon antenna, and near-field light is generated based on the surface plasmons. The near-field light generated by the plasmon antenna exists only within an area smaller than the diffraction limit of light. Irradiating the recording medium with the near-field light makes it possible to heat only a small area of the recording medium.
In a conventional thermally-assisted magnetic recording head, the plasmon antenna is directly irradiated with laser light, so that the plasmon antenna transforms the laser light into near-field light. In this case, there is the problem of poor use efficiency of the laser light since the laser light can be reflected at the surface of the plasmon antenna or can be transformed into thermal energy and absorbed by the plasmon antenna.
Having a size smaller than the wavelength of the light, the conventional plasmon antenna is small in volume. The conventional plasmon antenna therefore shows a large increase in temperature when absorbing the thermal energy. This results in problems such as the problem that the plasmon antenna expands and protrudes from a medium facing surface, a surface that faces the recording medium, to damage the recording medium.
To cope with this, there has been proposed the technique of arranging the outer surface of a plasmon generator, a piece of metal that generates near-field light, to face the outer surface of a waveguide (core) with a predetermined distance therebetween, and exciting surface plasmons on the plasmon generator by utilizing evanescent light that results from total reflection of the light propagated through the waveguide at the outer surface of the waveguide.
The thermally-assisted magnetic recording head can be configured so that the plasmon generator has an edge part that faces the outer surface of the waveguide with a predetermined distance therebetween. In such a configuration, a clad having a refractive index lower than that of the waveguide is interposed in part between the outer surface of the waveguide and the plasmon generator. In the foregoing plasmon generator, an end of the edge part that is located in the medium facing surface functions as a near-field light generating part. In the plasmon generator, surface plasmons are excited on the edge part based on the evanescent light occurring on the outer surface of the waveguide. The surface plasmons are propagated along the edge part to the near-field light generating part, and near-field light occurs from the near-field light generating part based on the surface plasmons. This configuration allows the surface plasmons excited on the edge part of the plasmon generator to be propagated efficiently to the near-field light generating part.
In the foregoing configuration, it is important to appropriately control the distance between the outer surface of the waveguide and the edge part of the plasmon generator in order to appropriately excite the surface plasmons on the edge part of the plasmon generator. In addition, in order to increase the recording density of the magnetic recording device, it is preferred that the near-field light be smaller in spot diameter. In order to reduce the spot diameter when the foregoing configuration is employed, it is effective to reduce the radius of curvature of the end of the edge part located in the medium facing surface.
The plasmon generator in the foregoing configuration can be formed by the following method. In the method, a dielectric layer is initially formed on the waveguide. Next, a groove that is V-shaped in cross section parallel to the medium facing surface is formed in the dielectric layer. The groove is formed so that its bottom does not reach the outer surface (top surface) of the waveguide. Next, a dielectric film is formed along the surface of the groove. The plasmon generator is then formed on the dielectric film. The dielectric layer and the dielectric film constitute part of the clad.
The above-described method of forming the plasmon generator has the problem that the distance between the outer surface of the waveguide and the edge part of the plasmon generator varies due to variations in the depth of the groove. The above-described method of forming the plasmon generator further has the problem that the edge part of the plasmon generator can be rounded, which makes it difficult to reduce the radius of curvature of the edge part, and consequently, it is difficult to reduce the spot diameter of the near-field light.